The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
A toothache is usually the result of poor dental hygiene, tooth cavities or decay, and injuries to the jaw or mouth. Sometimes, pain that's felt in the tooth is actually due to pain in other parts of the body, also known as referred pain. For example, an earache or nasal infection can sometimes cause tooth pain.